28 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



on the anterior face of the upper end. The outer half of the face is longer and 

 broader than the inner, which extends rather farther forward and is inclined 

 downward, forward, and slightly inward. The two halves of the face are much 

 more unequal than in Diadectes. The heavy proximal end contracts rapidly to a 

 relatively slender shaft, triangular in section. The distal end is expanded antero- 

 posteriorly, but is little wider than the shaft. The face is semilunar, due to a shal- 

 low concavity on the inner side of the distal portion of the shaft. The articular 

 surface is convex, presenting a posterior portion which looks almost directly down- 

 ward and an anterior, inclined upwardly and 

 inwardly; these two portions are not divided 

 into separate faces. 



The fibula is decidedly different in form 

 from the same bone in D. phaseoUnus. In that 

 animal the upper end of the bone is nearly cir- 

 cular in outline, joining the shaft below with a 

 sharp change in outHne. The lower part of the 

 bone widens gradually and the distal articular 

 surface is nearly flat (see fig. 30, p. 82, Publica- 

 tion 145, Cam. Inst. Washington). In Diaspa- 

 ractus the head is formed by a gradual widening 

 of the shaft and is very little thickened. The 

 outer edge of the whole bone is straight, nearly 

 to the distal end, where it turns slightly out- 

 ward; the inner border is quite concave, the 

 curve becoming sharper toward the distal end. 

 The distal end is considerably wider than the 

 proximal. There are two articular faces; one 

 larger, nearly horizontal, occupying nearly the 

 whole of the distal surface, and a smaller, inner 

 The whole bone is very thin, with slight con- 



FlG, 



16. Diasparaclus zenos Case, X 

 Upper surface of left hind foot. 



one, inchned upward and inward. 



cavities on the inner face just proximal to the edges. 



The tarsus of the left side is nearly complete and there is very Httle disturb- 

 ance; that of the right is less perfectly preserved. On the right side the tibiale 

 and fibulare and two bones of the distal row are in connection, but the tibiale is 

 badly injured. The tarsus, like the carpus, must have contained a considerable 

 amount of cartilage, for tarsaha I, II, III are mere nodules, while the pro.ximal 

 ends of the metatarsals are broad and heavy. The tibiale is much nearer in form 

 to that of Labidosaunis and the pelycosaurs than to that of Limnoscelis. Williston 

 describes the tibiale of Limnoscelis as a nearly cuboid bone which in his figure 

 occupies only the inner half of the distal articular face of the tibia. He regarded 

 it as either a tibiale or a tibiale +intermedium, but is inclined to believe that only 

 two bones may appear in the tarsus of the reptiles. In Diasparactus the tibiale 

 is rather elongate and, assuming the position in which the bone was found to be 

 correct, is roughly right-angled when seen from in front. The inner face (fig. 

 17 A, a), which was in contact with the fibulare as the bones lay, is wide and tri- 

 angular in outHne ; on the lower face of the horizontal portion there is a deep groove, 

 wider and deeper above and becoming shallower toward the lower edge. On the 

 lower part of the inner face there is another groove (fig. 17 a, b). The lower end 

 has a large, nearly square face, looking straight downward. The upper part of 

 the horizontal portion carries no articular face, but on the outer vertical edge 

 there are two rough faces, probably articular. The larger looks outward, upward. 



